Buckling protective fuze cap

ABSTRACT

A removable protective cap for an air driven fluidic fuze is described. A fluidic fuze having a plurality of ports therein for the introduction and exhaust of ram air is mounted in a projectile. A removable protective cap fits over the end of the fuze in sealing engagement with the parts during storage of the fuze and while the projectile is at rest in a launch tube or gun prior to firing. The protective cap includes a silicone rubber nose portion extending from one end of the fuze and a skirt portion which fits over the fuze end in sealing engagement with the ports. The cap further includes a shoulder portion between the nose and skirt portions. When the projectile is first fired, the setback forces in the launch tube cause the nose portion to be accelerated toward the wall of the tube. As the projectile emerges from the tube, the nose portion pivots about the cap shoulder as a fulcrum point in response to stored kinetic energy, and, if this is insufficient, to windstream drag forces to effect a complete removal of the protective cap.

United States atet n 1 Zimmerman Sept. 23, 1975 BUCKLING PROTECTIVE FUZE CAP [75] Inventor: Thomas H. Zimmerman, Reston,

22 Filed: Apr. 23, 1974 21 Appl. No.: 463,323

[52] US. Cl 102/81; 102/70 AC; 102/72 R; 102/78 [51] Int. Cl. F42C 5/00 [58] Field of Search 102/81, 81.2, 81.6, 78, lO2/80, 70, 70.2, 70 AC, 86, 76

[56] References Cited UNITED STATES PATENTS 1,416,856 5/1922 Mitzel 102/70 R 1,552,435 9/1925 Johnson 102/70 AC 1,666,672 4/1928 Varaud 102/80 1,850,196 3/1932 Bardsley..... 102/70 AC 2,023,938 12/1935 Savani 102/81 3,377,954 4/1968 Rabinow. l02/70.2 R 3,435,767 4/1969 Stav 102/70.2 R

FOREIGN PATENTS OR APPLICATIONS 154,467 2/1903 Germany 102/70 AC Primary E.raminer-Samuel Feinberg Assistant Examiner-Harold Tudor Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Saul Elbaum [57] ABSTRACT A removable protective cap for an air driven fluidic fuze is described. A fluidic fuze having a plurality of ports therein for the introduction and exhaust of ram air is mounted in a projectile. A removable protective cap fits over the end of the fuze in sealing engagement with the parts during storage of the fuze and while the projectile is at rest in a launch tube or gun prior to firing. The protective cap includes a silicone rubber nose portion extending from one end of the fuze and a skirt portion which fits over the fuze end in sealing engagement with the ports. The cap further includes a shoulder portion between the nose and skirt portions. When the projectile is first fired, the setback forces in the launch tube cause the nose portion to be accelerated toward the wall of the tube. As the projectile emerges from the tube, the nose portion pivots about the cap shoulder as a fulcrum point in response to stored kinetic energy, and, if this is insufficient, to windstream drag forces to effect a complete removal of the protective cap.

11 Claims, 3 Drawing Figures BUCKLING PROTECTIVE FUZE CAP RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured. used, and licensed by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION 1. Field of Invention The present invention relates to a protective cap for a fluidic fuze device for use in projectiles such as mortars and rockets. More specifically the present invention relates to a protective fuze cap for sealing the intake and exhaust ports of a fiuidic fuze during a storage or rest position, which is automatically removable from the fuze in response to setback and windstream forces when the projectile is fired.

2. Description of Prior Art Heretofore protective caps for fiuidic fuzes have taken various unsatisfactory forms.

In one example prior art protective caps have been formed of tempered glass which shatters into small particles at the time of firing. Caps of this type pose the potential problem of having small glass particles enter the fluidic ports rendering the fuze inoperative. Inaddition the glass particles may also present a hazard to the operator of the gun or launch tube and may in fact damage the bore of the gun.

Another type of prior art protective cap is fabricated from a material which ignites at firing and disintegrates. This type of cap poses a potential danger in that itinherently presents a fire hazard in storage.

Still another type of prior art protective cap is comprised of a material which tears apart from the setback forces at the time of firing. This type of cap is undesirable because the pieces of material torn from the cap may encounter the projectile as it moves through the gun bore. thereby causing damage to the bore and er ratic projectile flight, and because fragments of the torn cap may enter the fluidic ports and render the fuze inoperative.

Still another prior art device comprises a blow-by cap which is removed by propellant gases which fiow past the projectile in the tube. This blow-by cap suffers from the disadvantage that it is ineffective in newer mortar rounds which incorporate an obturating band to promote better projectile tube seal and therefore increase projectile range. This cap has shown a tendency to be unreliable when fired at certain charges where setback forces neutralize blow-by forces.

SUMMARY OF INVENTION Accordingly. it is an object of the present invention to provide a protective cap for a fluidic fuze which is removable by hand or automatically in gunfire without creating particles or fragments which can damage the gun bore. affect the projectile trajectory, or block the fluidic ports.

It is another object of the present invention to provide a protective cap for a fluidic fuze which presents no fire hazard during storage.

It is still another object of the present invention to provide a protective cap for a fiuidic fuze which does not rely on blow-by forces within the bore for removal thereof.

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The objects of the present invention are fulfilled by providing a removable silicone rubber cap which fits over the end of a fluidic fuze in sealing engagement with the air inlet and exhaust holes of said fuze. The rubber cap includes a nose portion extending from the end of the fuze, a skirt portion which fits over the end of said fuze in sealing engagement with said inlet and exhaust holes, and a shoulder portion disposed between said nose and skirt portions.

The rubber cap is designed to buckle in the gun barrel for launching the projectile in response to setback forces occurring at the time of firing. The buckling action is delayed until the projectile has transversed a part of the launch tube length and achieved a specified acceleration. When the cap buckles the nose portion is deflected towards the wall of the launch tube with a velocity that is too low to allow the nose to touch within the time frame that the projectile is inside the bore.

As the projectile emerges from the launch tube, the nose of the cap continues to deflect due to the kinetic energy accumulated during the buckling motion. The dimensions of the cap nose are chosen so that the stored kinetic energy is sufficient to overcome the work required to break the seal and dislodge the cap from the fuze. In addition, the dimensions are selected such that if propellant blow-by diminishes the available kinetic energy, then windstream drag forces complete the cap removal within the first few feet of projectile flight.

The minimum nose length (L) in inches necessary for buckling in response to setback forces can be calculated from the following formula:

( 15) where E modulus of elasticity of the material in pounds per square inch;

r= nose radius in inches;

G= setback Gs (Dimensionless); and

04 material specific weight in pounds per cubic inch.

The motions of the nose inside the launch tube during setback are determined from a computer routine such as NASTRAN.

In a preferred embodiment for a 60 mm mortar using silicone rubber L 2.0 inches.

BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION OF DRAWINGS Referring in detail to the drawings there is illustrated in FIG. 1, a fluidic fuze head generally designated 10. Fuze head 10 is provided with a dome shaped portion 12 which is substantially conical in a shape and which includes a waist portion 14. An air inlet hole is disposed in one end of fuze 10 at 16 and a plurality of air exhaust holes 18 are provided around waist portion 14.

Fluidic fuzcs such as are known in the art and operate in response to the forced flow of ram air through inlet hole 16 into the interior of the fuze whereby the energy of the ram air is converted into a mechanical or electrical energy for operating a detonating device. Ram air flows into hole 16 as the projectile carrying the fuze head travels through the air. Any excess air is exhausted through exhaust holes 18. In a preferred embodiment fuze head 10 is fabricated from a polycarbonate material.

It is the primary object of the present invention to protect fluidic fuze 10 from impurities and moisture which could enter the fuze head through holes 16, 18 during handling and storage, since these impurities and moisture could be detrimental to the operation of the fuze when the projectile is in flight. Accordingly, the need arises for a removable protective cap which fits over fuze head 10 in sealing engagement with inlet and exhaust holes or ports 16, 18, respectively.

Referring to FIG. 2 in detail there is illustrated the removable protective fuze cap 20 of the present invention and the manner in which it fits over fuze head 10 before firing of the projectile.

Cap 20 in a preferred embodiment is fabricated from silicone rubber and comprises a substantially solid nose portion 22 of a predetermined size, which extends from one end of fuze 10; a shoulder portion 24 at the base of nose portion 22 having at least one corner 24A; and a hollow sleeve or skirt portion 26 which fits over fuze head 10 in sealing engagement-with inlet and exhaust holes 16, 18. Skirt portion 26 has a base portion 28 which is molded to a smaller diameter than the rest of the skirt so that it snugly fits within waist portion 14 of fuze head 10 to thereby effect a good seal around the base of the skirt.

The high coefficient of friction between the polycarbonate fuze head 10 and silicone rubber cap 20 dictates the need for the use of a dry lubricant to assist in the insertion of cap 20 onto head 10. In preferred embodiments graphite or boron nitride lubricants have been found suitable for use.

It should be noted that the forces needed for removal increase with friction and as the seal is made tighter. The optimum dimensions for this particular seal configuration may be determined by equating the energy needed to completely dislodge the cap (experimentally determined) with the kinetic energy available for removal as the projectile leaves the gun. This value of kinetic energy may be found by modeling the cap for a computer routine such as NASTRAN, and determining the transverse velocity of the cap nose at the instant the projectile leaves the gun.

DESCRIPTION OF OPERATION The manner in which fuze cap 20 is removed in response to the firing of a projectile can be illustrated by reference to FIGS. 2 and 3.

FIG. 2 illustrates the positions of cap 20 and fuze 10 as each would be oriented in a gun barrel just prior to firing of the projectile. The direction of launch is in the direction of arrow A, as indicated in FIGS. 2 and 3.

The forward thrust of the projectile causes the cap nose to buckle and accelerate in axial and transverse directions. The nose portion 22 pivots about corner 24A of shoulder 24, as corner 24A is forced against dome-shaped surface 12.

FIG. 3 illustrates the position of the fuze cap 20 just after leaving the gun. The stored kinetic energy and applied windstream forces (direction indicated by arror B) force nose 22 to further pivot about corner 24A of shoulder 24 an additional amount until skirt 26 pops off of fuze head 10. This occurs within the first few feet of flight of the projectile. When this occurs air is free to flow through inlet and exhaust holes 16, 18 to facilitate the proper functioning of fluidic fuze 10.

An additional asset of the configuration is that the cap may be removed or replaced by hand should the need to do so arise.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications can be made by a person skilled in the art.

What is claimed is:

1. In combination with a fluidic fuze for a detonating device contained in a projectile to be fired from a gun, said fuze having at least one port in the exterior surface thereof for the flow of fluids therethrough, cap means for sealing said at least one port before said projectile is fired, said cap means being removable in response to forces generated by the firing of said projectile, the im provement in said cap means comprising:

a. a flexible nose portion of a predetermined size extending from one end of said fluidic fuze; and

b. a flexible skirt portion extending in the opposite direction from said one end over said fuze in sealing engagement with said at least one port; whereby the forces generated in response to the firing of said projectile cause said nose portion to pivot toward said skirt portion to thereby remove said skirt portion from said fuze.

2. The combination of claim 1 wherein said cap means is further provided with a shoulder means at the juncture of said nose portion and said skirt portion, said shoulder means serving as a fulcrum point about which said nose portion may pivot.

3. The combination of claim 2 wherein said forces generated by the firing of said projectile are' setback forces and windstream forces, said nose portion pivoting to a first position in response to said setback forces and a second position in response to said windstream forces.

4. The combination of claim 2 wherein said predetermined size of said nose portion is defined by the equation:

where E modulus of elasticity of the material in pounds per square inch;

i nose radius in inches;

G setback Gs (Dimensionless); and

a material specific weight in pounds per cubic inch.

5. The combination of claim 2 wherein the material of said cap means comprises silicone rubber.

6. The combination of claim 5 wherein the material of said fluidic fuze comprises a polycarbonate, and a dry lubricant is disposed between said cap and said fuze.

7. The combination of claim 6 wherein said dry lubricant is graphite.

8. The combination of claim 6 wherein said dry lubricant is boron nitride.

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9. The combination of claim 2 wherein said fluidie and a plurality of exhaust ports in the surface of said fuze is dome-shaped with a waist portion and a base waist portion portion of said skirt of said cap means is adapted to fit snugly within said waist to effect a seal.

10. The combination of claim 9 wherein said fluidic 5 fuze includes an entrance port for fluid in said one end 11. The combination of claim 1 wherein said cap is removable or replaceable by hand. 

1. In combination with a fluidic fuze for a detonating device contained in a projectile to be fired from a gun, said fuze having at least one port in the exterior surface thereof for the flow of fluids therethrough, cap means for sealing said at least one port before said projectile is fired, said cap means being removable in response to forces generated by the firing of said projectile, the improvement in said cap means comprising: a. a flexible nose portion of a predetermined size extending from one end of said fluidic fuze; and b. a flexible skirt portion extending in the opposite direction from said one end over said fuze in sealing engagement with said at least one port; whereby the forces generated in response to the firing of said projectile cause said nose portion to pivot toward said skirt portion to thereby remove said skirt portion from said fuze.
 2. The combination of claim 1 wherein said cap means is further provided with a shoulder means at the juncture of said nose portion and said skirt portion, said shoulder means serving as a fulcrum point about which said nose portion may pivot.
 3. The combination of claim 2 wherein said forces generated by the firing of said projectile are setback forces and windstream forces, said nose portion pivoting to a first position in response to said setback forces and a second position in response to said windstream forces.
 4. The combination of claim 2 wherein said predetermined size of said nose portion is defined by the equation:
 5. The combination of claim 2 wherein the material of said cap means comprises silicone rubber.
 6. The combination of claim 5 wherein the material of said fluidic fuze comprises a polycarbonate, and a dry lubricant is disposed between said cap and said fuze.
 7. The combination of claim 6 wherein said dry lubricant is graphite.
 8. The combination of claim 6 wherein said dry lubricant is boron nitride.
 9. The combination of claim 2 wherein said fluidic fuze is dome-shaped with a waist portion and a base portion of said skirt of said cap means is adapted to fit snugly within said waist to effect a seal.
 10. The combination of claim 9 wherein said fluidic fuze includes an entrance port for fluid in said one end and a plurality of exhaust ports in the surface of said waist portion.
 11. The combination of claim 1 wherein said cap is removable or replaceable by hand. 